The present invention relates to optical circuits and, more particularly, to systems and methods for fabricating refined flexible optical fiber circuits.
High capacity electronic systems are increasingly adopting optoelectronics as a means to surpass conventional limitations (e.g., transmission speed) of electrical interconnections. Although photonic technology has long been preferred in long-haul communications, optics is now quickly becoming a viable option for short link applications. One demanding short-link application for optical interconnection is in the interboard/shelf or backplane level of communication. Most large system equipment today is partitioned into bookshelf levels consisting of multiple printed wiring boards inserted into shelves within a frame or cabinet. One interconnect level within such a system is that between two printed circuit boards within the cabinet, known as the backplane level of interconnection.
Backplane systems are typically organized by mounting various system components on printed wiring boards and interconnecting the printed wiring boards with a circuit transmission element known as a backplane. The backplane may include various socket elements for receiving printed wiring boards. However, as the circuit density of printed wiring boards increases, it becomes difficult to provide the needed backplane interconnections because, as interconnection transmission lines become thinner, their impedances increase. Furthermore, electromagnetic interference between closely adjacent electrical signal parts can reduce signal integrity due to cross-talk and interference. Additionally, the distance over which information must be transmitted by backplane conductors is fairly long compared to the distances transmitted on printed wiring boards. These factors may reduce the speed at which the circuits can be operated, and the signal integrity, which may defeat a principal advantage of higher circuit densities. Optical fiber interconnections have been suggested to address these problems.
Recently, convenient and manufacturable methods of linking components at the backplane level via optical fiber interconnections have been suggested which may result in a number of advantages, including down-sized wiring closets, fewer cumbersome cables through management of connections, low loss distribution, and low cost. These optical fiber interconnections are often made of flexible material so that they can be bent for mounting in an appropriate structure to reduce the volume required by the system and to aid in connection to other electronic systems. Although advances in optical fiber J interconnections will be discussed with focus on implementation at the backplane level, these interconnections can be utilized in a number of short link applications other than simply those used as backplane connections within a large system cabinet.
U.S. Pat. No. 5,259,051, to Burack et al. (hereinafter Burack et al. ""051), assigned to ATandT Bell Laboratories, the predecessor in interest of the assignee of the present invention, which is incorporated herein by reference, describes a method for making optical circuits for use as backplanes by using a robotic routing machine to apply optical fiber to the flat surface of a flexible substrate that may be used as a backplane. The flexible substrate upon which optical fiber is routed is fastened or mounted onto a fixed backboard, or carrier plate, which provides support to the flexible substrate as a robotic machine routes and places optical fiber thereon. The routing machine of Burack et al. ""051 includes an elongated manipulator having a vertical axis and a wheel on the end thereof for applying optical fiber to the backboard-mounted flexible substrate. Attached to the vertical axis is a reel of optical fiber to be routed onto the flexible substrate. The vertical axis can be controlled to move in a plurality of directions, including in a rotatable direction around its axis, so that it can apply fibers to any portion of the substrate. As the vertical axis moves around the substrate, a continuous line of optical fiber is fed to the wheel on the end of the vertical axis, and deposited onto the flexible substrate. A controller operates the manipulator to achieve a desired pattern of optical fiber placed on the substrate. The layout of the optical circuit is preferably designed by a computer, which provides optical fiber routes of the appropriate length between input and output ports of the flexible substrate. Robotic routing machines are preferably utilized to implement these routes because it is often important for optical transmission reliability that there not be undesirable deviations in the prescribed length of each line.
While the methods and apparatuses of the Burack et al. ""051 patent have been implemented with great success, the creation of flexible optical fiber circuits using such a device results in lesser yield than is preferred because optical fibers are often cut by the robotic routing machine during the final stage of fabrication, which is the cutting of the final shape of the optical circuit. Because many customers demand optical circuits having narrow circuit tabs and precise substrate shapes, the creation and adherence to tight thresholds often results in the inadvertent cutting of an optical fiber, thus destroying the entire flexible optical circuit. This inadvertent cutting is often due to minor changes in the position of a substrate during different processing steps performed by the robotic routing machine. One reason for the problem is that it is often impossible to determine that an error exists in alignment until an optical fiber has already been cut and the circuit destroyed.
Accordingly, there is a continuing need for methods and systems that maximize fabrication yield of flexible optical fiber circuits using of robotic routing machines.
The present invention uses one or more optical fiber test patterns routed on a substrate to ensure that a robotic routing and cutting machine is properly aligned before the routing machine makes precise cuts very close to optical fiber placed on a substrate by the machine. Using the test patterns avoids alignment errors that may otherwise occur during the cutting of the optical fiber circuit which can result in a total loss of the optical fiber substrate.
According to one embodiment of the invention there is disclosed a method for fabricating flexible optical fiber circuits. The method comprises routing optical fiber on a flexible substrate according to a predetermined pattern using an optical fiber routing head, wherein routing the optical fiber includes routing at least one non-disposable optical fiber portion and least one disposable optical fiber portion. The method also comprises aligning a cutting head to cut adjacent the non-disposable optical fiber portion, wherein aligning the cutting tool is based upon the accuracy with which the cutting head cuts adjacent to the disposable optical fiber portion.
According to one aspect of the invention, the at least one disposable optical fiber portion comprises at least one test pattern. According to another aspect of the invention, the at least one disposable optical fiber portion is continuous with respect to the at least one non-disposable optical fiber portion. According to yet another aspect of the invention, the flexible substrate is perforated prior to routing optical fiber on the flexible substrate, and an adhesive may be provided on a surface of the flexible substrate prior to routing the fiber on the substrate. Additionally, the optical fiber may be coated on the flexible substrate using a conformal coating. Moreover, after the cutting head is aligned, a cut may be made adjacent the non-disposable optical fiber portion to fabricate the flexible optical fiber circuit.
According to another embodiment of the invention, there is disclosed a system for fabricating flexible optical fiber circuits. The system includes at least one flexible substrate, and optical fiber routed on the at least one substrate, wherein the optical fiber includes at least one non-disposable portion and at least one disposable portion, and wherein the at least one disposable portion includes at least one optical fiber test pattern. The system further includes a routing machine, comprising a cutting tool configurable to cut the at least one flexible substrate to fabricate a flexible optical fiber circuit, wherein the at least one routing machine utilizes the at least one optical fiber test pattern to align the cutting tool with respect the at least one non-disposable portion of the optical fiber.
According to one aspect of the invention, the system further comprises at least one aligning post for aligning the at least one flexible substrate with respect to the routing machine. Additionally, the routing machine may further include a control unit, wherein the control unit automates the movement of the cutting tool. According to another aspect of the invention, the optical fiber test pattern is continuous with the at least one non-disposable portion.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such features and advantages be included herein within the scope of the present invention as defined by the appended claims.